The Central Nervous System

The Central Nervous System
The Brain & Spinal Cord
Chapter 13
Meninges
20
days
28
days
35
days
Forebrain telencephalon (cerebrum - the cerebral hemispheres)
diencephalon (thalamus, hypothalamus)
Midbrain mesencephalon (tubular, upper brain stem)
Hindbrain metencephalon (pons, cerebellum)
myelencephalon (medulla oblongata, lowest part of brain stem)
Cerebrum (telencephalon)
85% of brain mass
Function(s): perceive
information, direct motor
responses, memory,
center of intellect,
language, consciousness
Cerebrum is subdivided by
convolutions into itself.
Sulcus – grooves or depressions
Fissure – deep sulci
Gyrus – rounded elevations
Longitudinal fissure – divides
cerebrum into the R and L
hemispheres.
Transverse fissure –
separates cerebrum from
cerebellum
Central sulcus – separates the
frontal lobe from the parietal
lobe.
Precentral gyrus – voluntary
movement
Postcentral gyrus - pain
Transverse
fissure
Lobes of the Cerebrum
Frontal – “somatomotor” functions
(voluntary movement), intellectual
functions, aggression, sexual behavior,
olfaction, motor area, Broca’s area of
speech (on left side only; coordinates
speech muscles)
Parietal – abstract reasoning
(mathematics), use of symbols for
communication (“language”), body
sensory awareness including taste,
touch, temperature, pressure, pain
Occipital – vision “visual cortex”,
receives, interprets and discriminates
visual stimuli from the optic tract.
Temporal – auditory area “auditory
cortex”, formation of emotions, memory
processing.
Lateral view
Medial view
Cerebral Cortex
Gray matter – unmyelinated, outer surface (2-5 mm thick). Contains 75% of nueron
cell bodies. Follows the sulci, gyri and fissures of cerebrum.
White matter – located under cortex, comprises bulk of cerebrum. Consists of
bundles of myelinated nerve fibers.
White matter – 2 major types of white matter fibers
Commissures – tracts of fibers connecting left and right hemispheres, largest is the
corpus collosum. This tract covers both hemispheres and is roofing over the
lateral ventricles.
Association fibers – bundles of white matter that connect anterior and posterior
cortical area.
Projection fibers – connects cortical area with lower brain and spinal cord.
Sensory input reaches cortex through these fibers.
Thalamus and cortex communicates by this pathway.
Forms corona radiata.
Projection fibers – corona radiata is largest mass of white matter in brain.
Basal nuclei (ganglia) are areas of gray matter buried deep in white matter.
Help regulate and coordinate aspects of movement, especially starting and stopping
voluntary movement. Also regulates the intensity of movements.
Parkinson’s Disease – basal nuclei provide too little motor drive, slow movement/tremors
of limbs.
Huntington’s Disease – overstimulation of the motor drive, limbs jerk unstoppably.
Ventricles – expansions of the brain’s central cavity filled with cerebrospinal fluid.
Lateral ventricles – lie in cerebral hemispheres.
Third ventricle – lies in diencephalon.
Fourth ventricle – lies in hindbrain.
Cerebral aqueduct – lies in mesencephalon. Connection for 3rd and 4th ventricles.
Cerebrospinal Fluid
• A clear, largely acellular fluid with less
density and protein than plasma.
• Provides shock-absorbing function.
• About 150 ml. Excess production of CSF or
lack of drainage can cause hydrocephaly.
• CSF is secreted by specialized capillaries
from the pia mater called choroid plexuses.
Route of Circulation
• I and II ventricles to the III ventricle to the IV ventricle to
the spinal cord and subarachnoid space.
• CSF is reabsorbed in arachnoid villi into the blood filled
superior sagitall sinus (dural sinus).
Diencephalon – forms the central core of the forebrain and is surrounded by the cerebral
hemispheres. Consists of 3 paired structures (thalamus, hypothalamus, epithalamus.
Thalamus – egg shaped, dense gray matter, forms superolateral wall of 3rd ventricle.
12 major nuclei with axons that reach the cortex. Processes all incoming impulses from
sensory pathways (except olfactory). “gateway to cerebral cortex”
Diencephalon – forms the central core of the forebrain and is surrounded by the cerebral
hemispheres. Consists of 3 paired structures (thalamus, hypothalamus, epithalamus)
Epithalamus – secretes melatonin which induces sleep.
Hypothalamus – controls autonomic nervous system, emotional response, behavior,
endocrine system. Regulates body temperature, hunger, thirst sensations, sleep-wake
cycles. Formation of memory.
Epithalamus
The Brain Stem – midbrain, pons and medulla oblongata.
Midbrain (mesencephalon) – short section between diencephalon and pons. Acts as a
relay center between forebrain and hindbrain. Cerebral aqueduct passes through here.
Pons (part of metencephalon) – relay of impulses to and from the medulla oblongata and
the cerebrum and between cerebrum to cerebellum.
The Brain Stem – midbrain, pons and medulla oblongata.
Medulla oblongata (myelencephalon) – continuation of the superior portion of the spinal
cord and forms the inferior part of the brain stem. Begins at foramen magnum continues
superior.
Contains all ascending (sensory) and descending (motor) white matter tracts that
connect the spinal cord with the brain.
medulla oblongata: Vital and non-vital body functions.
Vital Functions – respiration center (pattern and rate), cardiac center (rate and force),
vasomotor center (blood vessel diameter, blood pressure regulation by smooth muscle
stimulation or inhibition).
Non-vital Functions – sneezing, coughing, vomiting, swallowing, hiccuping. Many of
these are controlled by the hypothalamus.
The Brain Stem – midbrain, pons and medulla oblongata.
Axons cross over (R and L) such that the right cerebral cortex controls muscles on the
left side, etc.
Cerebellum (metencephalon) – 2nd largest portion of brain. Located below occipital lobe,
posterior to pons. Made up of 2 lateral hemispheres, gray matter at surface and deep
white matter.
Cerebellum (metencephalon) – Functions are equilibrium and position sense, fine
movement, control of muscle tone and overall coordination of muscular activity in
response to proprioreceptive input (coordinates antagonistic muscles).
The Spinal
Cord
Basic structure of the spinal cord in cross section.
2 median grooves: A deep anterior median fissure and a shallow
posterior median sulcus. These extend length of cord forming lateral
halves.
posterior median sulcus
anterior median fissure
DRAW!
The basic structures of the spinal cord show lateral symmetry, with white
matter on the outside and gray matter on the inside.
posterior median sulcus
White matter
Gray matter
anterior median fissure
Gray matter (“butterfly”) consists of neuron cell bodies, synapses,
nonmyelinated neurons (interneurons, neurons that connect sensory and
motor neurons that acts as a reflex processor).
posterior median sulcus
White matter
Gray matter
anterior median fissure
Gray matter:
Ventral Horn (anterior horn) – contains cell bodies of motor neurons. Motor
information out through axons that leave the ventral root.
posterior median sulcus
White matter
Gray matter
Ventral horn
anterior median fissure
Gray matter:
Dorsal Horn (posterior horn) – contains interneurons. Receives sensory
input from sensing neurons whose cell bodies lie in the dorsal root ganglia
and axons enter the dorsal root.
posterior median sulcus
Dorsal horn
White matter
Gray matter
Ventral horn
anterior median fissure
Gray matter:
Gray commissure – horizontal bar connecting the wings of the gray matter.
Connects right and left sides.
posterior median sulcus
Dorsal horn
White matter
Gray matter
Gray comminsure
Ventral horn
anterior median fissure
Gray matter:
Lateral horn – smaller lateral protrusion found in thoracic and lumbar levels
only. Autonomic motor neurons to smooth and cardiac muscle, and glands.
posterior median sulcus
Dorsal horn
White matter
Gray matter
Lateral horn
Gray comminsure
Ventral horn
anterior median fissure
Central canal – continuous with ventricles of brain and contains spinal fluid.
Canal disappears before adulthood.
posterior median sulcus
Dorsal horn
White matter
Gray matter
Lateral horn
Gray comminsure
Central canal
Ventral horn
anterior median fissure
White columns (matter) – consists mostly of myelinated neurons. Divided
by gray matter in three distinct regions (anterior, posterior, lateral funiculi)
that contain longitudinal bundles of nerve fibers (axons).
posterior median sulcus
Dorsal horn
White matter
Gray matter
Lateral horn
Gray comminsure
Central canal
Ventral horn
anterior median fissure
White columns (matter) –
Ascending tract – sensory (afferent) into to brain. Pain relief?
Descending tracts – motor (efferent) info from brain to muscles/glands.
Ascending tracts
(senory in)
posterior median sulcus
Dorsal horn
White matter
Gray matter
Lateral horn
Gray comminsure
Central canal
Descending tracts
(motor out)
Ventral horn
anterior median fissure
Direction of movement of messages:
Gray matter – horizontal
Ascending tracts
(senory in)
White matter - vertical
posterior median sulcus
Dorsal horn
White matter
Gray matter
Lateral horn
Gray comminsure
Central canal
Descending tracts
(motor out)
Ventral horn
anterior median fissure